1. Technical Field
The present invention relates to an image forming apparatus such as electrophotographic copiers, printers, and facsimiles.
2. Related Art
Conventional image forming apparatus provided with plural submodules such as a photoconductor drum, a charging device, an exposure device, a developing device, and a transfer device is known. In this image forming apparatus, the rotating photoconductor drum is uniformly charged by the charging device. Then, the charged surface of the photoconductor drum is selectively illuminated with light by the exposure device, thereby an electrostatic latent image is formed on the photoconductor drum. After the electrostatic latent image formed on the photoconductor drum is developed into a visible image by the developing device, the thus produced toner image is transferred onto a recording material by the transfer device.
In this image forming apparatus, to suppress non-uniformity in the density of an image recorded, a toner image of a predetermined pattern is formed at predetermined timing and operating parameters of the submodules constituting the image forming apparatus are adjusted, based on results of detecting the density of the toner image of the predetermined pattern. These operating parameters may include, for example, a charging bias that is used by the charging device, the light quantity of a light beam that is emitted by the exposure device, a developing bias that is used by the developing device, the amount of toner supply, and output power of the transfer device.
In the image forming apparatus, certain tolerances are allowed for the photoconductor drum and a photoconductive layer formed on the drum. For this reason, even if the above operating parameters are set appropriately, non-uniformity in density may occur in the rotation direction of the photoconductor drum, or in other words, in a slow-scan direction. Besides the photoconductor drum, certain tolerances are allowed for, for example, a charging roller provided in the charging device, a developing roller provided in the developing device, and a transfer roller provided in the transfer device, respectively. Therefore, these submodules may be a possible source causing non-uniformity in density in the slow-scan direction during the formation of an image.
Especially, still higher image quality is required recently and there is a need to improve uniformity in density at a high level, which has not been acknowledged as a problem in the past. In short, non-uniformity in density in the slow-scan direction caused by these plural submodules is a new emerging problem.